Vascular occlusions restrict the flow of blood to tissue and organs and can cause a variety of problems. For example, occlusions that restrict blood flow to the heart can cause heart attacks and angina, and occlusions that restrict blood flow in cerebral blood vessels (e.g., cerebral arteries and veins) can cause strokes and other neurological problems. It is therefore desirable that these occlusions be opened up and removed.
One approach to treating occlusions is to apply drugs that cause the vessel to dilate. However, these drugs are not suitable for all patients, and even when they are suitable their ability to slow and reverse the occluding process is usually only temporary. Drugs may also be administered that dissolve occlusions. However, these drugs can cause serious side-effects, such as hemorrhaging, and do not dissolve many types of vascular occlusions.
Another approach to treating occlusions is angioplasty, where a device (typically a catheter) for dilating an occluded vessel is introduced through an opening in the skin and wall of a large vessel, such as the brachial or femoral artery. When the device reaches the site of the occlusion, treatment is administered to break up or otherwise treat the occlusion. For example, in balloon angioplasty a guide wire first reaches the site of the occlusion and guides a catheter lumen to the site. The catheter lumen has an inflatable balloon near its tip that inflates to compact the occlusion and stretch the walls of the vessel. Unfortunately, the results of balloon angioplasty can also be temporary as the occluding process may continue and re-block the vessel.
Additional approaches to treating occlusions include recanalizing the occlusion by cutting and/or pulverizing the occlusion with a vascular catheter. Here also guide wires may first reach the occlusion site and guide a catheter lumen to the occlusion. The guide wire tips are designed to be relatively small and stiff so that they can more easily penetrate and advance through the occlusion, providing a path or rail for the subsequently advancing catheter to follow through the occlusion. When the catheter reaches the occlusion, a device at the catheter's distal tip is advanced into the occlusion where it performs the operation to cross or penetrate the occlusion. The catheter may also include components that capture, suction or otherwise prevent the occlusion fragments from traveling downstream and creating another blockage. These approaches are relatively effective for treating acute occlusions made of relatively soft tissue and occlusions that do not completely block the passage of blood and other fluids through the vessel, but are less effective for treating calcified, fibrotic occlusions that are difficult to penetrate with conventional guide wires.
Vascular occlusions may also be treated by ablation with light energy (e.g., laser atherectomy). These approaches involve positioning optical fibers at the site of the occlusion and delivering light energy through the fibers to ablate the occlusion. The optical fibers are typically made of fused silica or quartz, and are fairly inflexible unless they are made very thin. Unfortunately, thin optical fibers can only deliver small amounts of light energy to the occlusion site. Also, the thin delicate fibers are easily damaged during ablation of hard occlusion materials like calcified deposits. Moreover, the light energy is attenuated over a relatively short distance as it passes through a small optical fiber. Thus, there is a need for new approaches to deliver light energy to a vascular occlusion.